Neospora caninum serostatus and milk production of Holstein cattle

OBJECTIVE: To determine whether Neospora caninum serostatus was associated with milk production among Holstein cattle in Ontario. DESIGN: Case-control study and cross-sectional observational study. ANIMALS: 3,702 Holstein cows in 83 herds (case-control study) and 3,162 Holstein cows in 57 herds. PROCEDURE: Herds in the case-control study were grouped on the basis of N. caninum abortion status. Herds in the observational study were considered representative of Ontario dairy herds. The N. caninum serostatus of individual cows was determined with a kinetic ELISA. Milk production was modeled to compare seropositive with seronegative animals while controlling for parity, days since parturition, and herd clustering. RESULTS: In the case-control study, 305-day milk production of seropositive cows was significantly less than milk production of seronegative cows in herds with abortions attributable to N. caninum infection and in herds with abortions attributable to pathogens other than N. caninum, but not in herds without abortion problems. In the observational study, 305-day milk production for seropositive cows was not significantly different from milk production of seronegative cows. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the association between N. caninum serostatus and milk production in Ontario Holstein dairy cattle may depend on abortion status of the herd. In herds with abortion problems, regardless of cause, N. caninum-seropositive cattle produced less milk, whereas in herds without abortion problems, N. caninum-seropositive cattle produced the same amount of milk as seronegative cattle.     

Herd-specific and age-specific seroprevalence of Neospora caninum in 14 British dairy herds.

All the cattle in 14 dairy herds in England were tested for Neospora caninum-specific antibodies with a commercial ELISA. Three of the herds had had sporadic abortions, eight had had endemic abortions and three had had epidemic abortions associated with N caninum before the study. Of 4295 cattle tested, 17.1 per cent were seropositive and the herd-specific prevalence ranged from 7.3 per cent to 44.8 per cent. No significant effect of either herd size (P = 0.988), endemic (P = 0.869) or epidemic (P = 0.138) patterns of abortion on herd-specific prevalence was found by using logistic regression analysis. There was no evidence in any herd of a significant increase in prevalence with age; the prevalence in seven-to 12-month-old cattle was not significantly different (P > 0.400) from the prevalence in older cattle, except that there was a significantly lower prevalence (P = 0.017) in 13-to 24-month-old cattle. The results of this study are consistent with vertical transmission being the major route of N caninum transmission in these herds.     

Serological evidence of Neospora caninum in dual-purpose cattle herds in Venezuela

Bovine neosporosis is a parasitic disease produced by Neospora caninum that induces abortion in cows, and consequently has a negative impact on the herd's reproductive efficiency. The main objective of this research was to determine the serological evidence of N. caninum in cattle herds from Venezuela using an indirect antibody capture ELISA test. Four hundred and fifty-nine (459) serum samples from crossbred adult cows were collected to be tested for Neospora antibodies. The sampled cows came from 15 large farms located in eight important cattle states that have predominant dual-purpose production systems (cattle from these farms are used for both milk and meat production). Fifty-two cows (11.3%) were seropositive to N. Caninum. Thirteen (86.7%) of 15 studied herds had cows seropositive to N. caninum. The average within-herd seroprevalence was 11.5% (range 3.8-36.7%). Cows that aborted in some of these farms had 2.71 (P: 0.009) greater odds to be seropositive when compared to cows that did not abort. Each one of the eight states represented in our study had seropositive animals. These results are the first evidence of exposure to N. caninum in Venezuelan cattle herds, indicating the possible circulation of this pathogen in the country. Further epidemiological studies should be granted to determine the spread of the disease in the Venezuelan cattle industry and its associated risk factors.     

Investigation of Neospora sp. antibodies in aborted mares from Normandy, France

Neospora caninum, an apicomplexan protozoan parasite, is recognized as a major cause of abortion in cattle while limited information is presently available on association between equine Neospora infections and abortions. The aim of the present study was to document prevalence of antibodies against Neospora sp. in aborted mares as a clue to the role of N. caninum in mare reproductive failure in Normandy, France. Using an agglutination test, the number of animals with elevated (>80) anti-Neospora sp. antibody titer was higher in a group of 54 aborted mares than in randomly chosen groups of 45 mares and 76 horses sampled for equine arteritis virus and Fasciola hepatica antibodies, respectively (P<0.001). N. caninum DNA was found in 3/91 fetal brains, 2/77 fetal hearts, and 1/1 placenta, and present in both brains and hearts of two fetuses. In 13 cases for which both mare serum and fetus were available, no fetal N. caninum amplification product was present while a large variation of maternal antibody titers was found. Data prompt at additional surveys of association between equine reproductive failure and Neospora sp. infection.     

Epidemiology and impact of Neospora caninum infection in three Queensland tropical dairy herds

This study investigated the epidemiology of Neospora caninum in three tropical dairy herds in North Queensland, Australia. All animals in the herds were bled, and the sera were tested by ELISA for N. caninum antibodies. Herd records were examined, and the number of calves carried to term and the number of abortions which occurred over the lifetime of each animal were recorded to determine the abortion rate for each animal. Pedigrees were constructed for two of the herds to investigate whether vertical transmission was occurring. The seroprevalence of N. caninum ranged from 23% to 34%. The abortion rate in seropositive animals was significantly (p < 0.001) higher than in seronegative animals in all three herds (12-20.1% cf. 3.6-7%). Overall, the probability of a calf being seropositive was 3.5 times higher when the dam was also seropositive than when the dam was seronegative. Subsequent selective breeding employed by one herd reduced the N. caninum seroprevalence from 23% to 5% over a 9-year period. This study shows that N. caninum infection is prevalent in North Queensland dairy cattle, and both post-natal infection and vertical transmission are common.     

Seroprevalence of Neospora caninum and abortion in dairy cows in northern Spain.

The seroprevalence of Neospora caninum infection was estimated from a sample of 889 cattle from 43 dairy herds in three counties in the Asturias region of Spain. The true prevalence of infection was estimated to be 30.6 per cent (95 per cent confidence interval (CI) 27.6 to 33.6). Seropositivity was associated with abortion during the previous year (odds ratio (OR)=3.31, P<0.001) and was slightly higher among purchased cattle (37.6 per cent), than among cattle raised on the farm (29.1 per cent) (P=0.078). Seropositive cows were more likely than seronegative cows to have had a seropositive dam (OR=2.3, P=0.011), suggesting that congenital transmission contributed to about 56 per cent of the infections. Herds with a true seroprevalence above 10 per cent had more dogs on the farm, than herds with a lower prevalence (P=0.032). The ORS relating abortion to seropositivity in individual herds ranged from 0.7 to 19, indicating that some herds experienced few abortions caused by N. caninum, while others experienced more abortions due to the organism. Overall, 38.7 per cent of the abortions were estimated to have been attributable to N. caninum.     

Outbreak of abortion associated with Neospora caninum infection in a beef herd

Abortion outbreaks caused by infection with Neospora caninum in beef cattle have not been well documented. Neospora caninum infection was confirmed in 4 fetuses that were aborted by cattle in a 350-head beef herd; an additional 58 cattle aborted during the next 2.5 months. Overall, 44.4% (157/354) of the cattle in the herd did not become pregnant or experienced fetal loss during this period. Initially, 81.3% (282/347) of the herd was seropositive for antibodies to N caninum, and seropositive cows were 6.2 times as likely to not be pregnant as were seronegative cows. Other potential causes of abortion were not identified in this herd. Following the outbreak, few cattle in the herd or in a second exposed herd seroconverted, but high antibody titers persisted in most seropositive cattle through the end of the calving season. Evidence of cow-to-fetus transmission of the organism was detected in > 82% of seropositive cows.     

Serological prevalence of Neospora caninum in healthy and aborted dairy cattle in Mashhad, Iran

A total of 810 dairy cattle were blood sampled and used to evaluate serological screening for Neospora caninum infection in dairy cattle herds in Mashhad (Khorasan province, Iran). In 4 herds, of the 810 cattle, 123 (15.18%) were seropositive by IFA Test (VMRD Inc., Pullman, WA 99163, USA) with titer 1:200 and range of prevalence per herd from 9.92 to 19.60%. Seroprevalence was not significantly different between Holstein breed (14.88%) and Brown Swiss breed (19.60%). Comparison of N. caninum serological status with age groups (< or =2 years, 2-4 years, > or =4 years) showed no significant difference. Of the 139 aborted cattle sampled, 19.42% were seropositive for N. caninum.     

Diagnostic significance of Neospora caninum DNA detected by PCR in cattle serum

A nested PCR that successfully detected Neospora caninum DNA in serum of cattle was used for investigation of selected abortion cases and in a study of healthy pregnant cows at an abattoir. N. caninum DNA was not detected in serum from antibody positive dams that aborted due to N. caninum, but was present in serum of some antibody negative dams that aborted due to other causes. N. caninum DNA was also found in the serum of about half of the animals that aborted of undetermined cause, but was not detected in cow sera from two beef cattle herds in Western Australia with no recent history of abortion. In the abattoir study of 79 dams and their foetuses N. caninum DNA was found in serum of 3 dams and in material from 11 foetuses. The majority of the cows and all foetuses were antibody negative. Our findings suggest that there is no obvious relationship between the presence or absence of N. caninum DNA in serum and the presence of antibodies to N. caninum in dams, the presence of N. caninum DNA in foetuses or abortion due to N. caninum. This is the first report of the detection of N. caninum DNA in serum of cattle rather than the white blood cell fraction. It indicates the presence of free tachyzoites and/or parasite DNA in circulation. The results suggest that persistent infection in the absence of antibodies is a possible outcome of N. caninum infection. Infection of foetuses in the absence of antibodies supports the possibility of persistent infection due to immunotolerance to an early in utero infection. It is therefore important to test for N. caninum DNA as well as antibodies for the detection of exposed and/or infected animals. However, the presence or absence of N. caninum antibodies or DNA did not support nor exclude N. caninum as the cause of abortion. Additional criteria are required for a positive diagnosis of abortion caused by N. caninum.     

Proportion of abortions due to neosporosis among dairy cattle in Japan

A retrospective cohort study was conducted to clarify the association between seropositive reactions to Neospora caninum and subsequent reproductive disorders among dairy cattle in Japan. A statistically significant association between Neospora seropositive reactions and abortions was observed (P=0.016), and seropositive cattle were 6.1 times more likely to abort compared to seronegative cows. No significant differences were observed between seropositive reactions and other reproductive disorders such as conception failure, perinatal death and calf mortality. As indicated by estimation of the attributable fraction, 83.6% of abortions in Neospora seropositive animals may be attributed to N. caninum. Considering seroprevalence of N. caninum in the cattle which aborted in Japan, 21.8% of abortions were estimated to be caused by neosporosis in Japan.     

Efficacy of a Neospora caninum killed tachyzoite vaccine in preventing abortion and vertical transmission in dairy cattle

A clinical trial was undertaken to assess the efficacy of Bovilis(?) Neoguard, a killed Neospora caninum tachyzoite vaccine on 5 commercial dairy farms in New Zealand with a history of Neospora-associated abortion. Cattle were enrolled in the trial at 30-60 days of gestation and randomly allocated to treatment or control groups. Treatment consisted of 5 mL doses of Bovilis Neoguard administered subcutaneously at enrolment then 4 weeks later. Isotonic saline was administered to the control group. Of 2246 cattle enrolled in the trial, 10.7% of cows and 12.6% of heifers were seropositive to N. caninum. Sampling of a randomly selected proportion of enrolled animals 6 weeks after the second treatment showed that 188/232 (81.0%) vaccinated with Bovilis(?) Neoguard had seroconverted, while 11/130 (8.5%) cows and 10/36 (27.8%) heifers in the control group had seroconverted. Forty-eight vaccinated and 63 control animals aborted. On one farm 12.5% of control animals and 6.1% of vaccinated animals aborted (vaccine efficacy 0.61; p=0.03). On another farm with a high level of abortion 8.4% of control animals and 8.7% of vaccinates aborted. On the remaining 3 farms fewer abortions occurred than expected. A modified Poisson regression approach was used to calculate relative risks for abortion and vertical transmission. Overall vaccine efficacy was 0.25 (p=0.12). Heifer replacement calves from the animals enrolled in the trial were sampled for antibodies to N. caninum at 6-9 months of age. Fourteen of 17 calves from vaccinated, seropositive cows were seropositive as were 13/23 calves from seropositive cows in the control group. The interaction between dam serostatus and treatment group was significant (p=0.05) with vaccination increasing the risk of vertical transmission. It was concluded that vaccination after conception prevented 61% abortions in one of five herds and that vaccination may have increased the risk of early embryonic death.     

Neospora caninum and bovine virus diarrhoea virus infections in Swedish dairy cows in relation to abortion

The protozoan parasite Neospora caninum and bovine virus diarrhoea virus (BVDV) are recognized as important causes of bovine abortion and congenital disease worldwide. In this study, serological investigations were performed to estimate the prevalence of N. caninum infection in Swedish dairy cattle, to assess to what extent it may affect abortion rates, and to determine possible effects of coinfection with BVDV. The overall N. caninum seroprevalence in Swedish dairy cows was estimated at 2% (16/780), and the BVDV seroprevalence was 32% (249/780). Among aborting cows from herds with abortion problems, 7% (26/378) had antibodies to N. caninum and 42% (153/378) to BVDV. Seventeen of the N. caninum positive animals also had antibodies to BVDV. There was a statistically significant (P = 0.013) association between presence of antibodies to N. caninum and BVDV. In a case-control study comprising sera from cows in herds without recognized abortion problems, 6% (5/89) and 1% (1/89) of sera from aborting and non-aborting cows, respectively, had antibodies to N. caninum. Two of the N. caninum seropositive aborting cows also had antibodies to BVDV. These results confirm that N. caninum infection is associated with bovine abortion in Sweden and also indicate that there might be concurrent effects of N. caninum and BVDV. It is concluded that Swedish dairy cows have a low prevalence of N. caninum infection which is favourable in relation to possible future control programmes.     

Risk of abortion associated with Neospora caninum during different lactations and evidence of congenital transmission in dairy cows

OBJECTIVE: To examine the relationship between exposure to Neospora caninum and abortion in dairy cows during their first, second, third, and fourth or later lactations and to establish the main mode of transmission in female calves from birth until their first pregnancy was terminated by abortion or parturition. DESIGN: Prospective observational study. ANIMALS: 460 Holstein cows and 79 female calves. PROCEDURE: Cows were classified as seropositive or seronegative to N caninum within 7 days after calving; incidence of abortion was compared between groups during different lactations. Blood samples were collected from female calves before ingestion of colostrum and every 6 months until their first pregnancy was terminated by abortion or parturition; number of seropositive calves was compared between seropositive and seronegative dams. RESULTS: During the first pregnancy of their second lactation, risk of abortion for seropositive cows was 2.8 times that of seronegative cows. Among 10 calves born to seropositive cows, 4 were classified as seropositive at birth and thereafter. Among 69 calves born to seronegative cows, all were classified as seronegative at birth; 67 calves remained seronegative thereafter. CONCLUSIONS AND CLINICAL RELEVANCE: Exposure to N caninum alone was not significantly associated with abortion in cows during the first, third, and fourth or later lactations. Seropositive cows that have aborted previously may have subsequent abortions attributable to N caninum. Congenital infection was the main mode of N caninum transmission in a cohort of female calves.     

Seroepidemiology of neosporosis in dairy cattle in Uruguay

A seroepidemiological survey of Neospora caninum was done in a dairy farm in Uruguay employing indirect fluorescent antibody test (IFAT). Sera from 217 cattle (155 cows, 31 heifers and 31 calves) were tested for N. caninum antibodies in July 2000 and it was found that abortions were significantly associated with the seropositivity of the cows by chi(2)-test (P = 0.025). The cows with an IFAT titre of 1:3200 were at a significantly higher risk of abortion than seronegative cows (P = 0.0013). Neospora organisms were detected in the brains of two aborted foetuses by immunohistochemical examination. The infection of N. caninum was considered postnatal because of the even distribution of seropositive cows (60%), low seroprevalence (20%) in calves and no significant correlation in the serostatus between calves and their dams (P = 0.43). A fitted binomial generalised linear model revealed that there was an increasing risk of abortion with increasing IFAT titre and increasing age between 2 and 6 years.     

Seroepidemiology of Neospora caninum infection in dairy cattle herds in Mashhad area, Iran

A seroepidemiology study of Neospora caninum was conducted in Mashhad area, Khorasan province, Iran on 337 cattle from 30 dairy using ELISA. All herds had seropositive cattle and antibodies were formed in 46% of the cattle. Abortion was significantly associated with seropositivity of cattle. The highest risk of abortion was observed in the 1-2-year-old cows. Our results indicate that Neospora infection is widespread in Iran.     

Associations between pregnancy outcome and serological response to Neospora caninum among a group of dairy heifers

AIM: To monitor pregnancy in a group of rising 2-year-old dairy heifers on a farm on which abortion due to Neospora caninum was known to occur in previous years. METHODS: A prospective cohort study group of 164 rising 2-year-old heifers was pregnancy-tested and blood-sampled at 4-5-week intervals throughout gestation. Sera were tested for antibodies to N. caninum at 3-4-month intervals, using an enzyme-linked immunosorbent assay (ELISA). When loss of pregnancy was detected, an N. caninum indirect fluorescent antibody test (IFAT) was conducted retrospectively on stored sera collected the month before abortion, the month abortion was detected, and for the following 2 months, from heifers that aborted. All fetal and placental material detected following abortion was subjected to gross post-mortem and histopathological examination. RESULTS: Eleven of 18 (61%) heifers that were seropositive and 4/146 (3%) heifers that were seronegative to N. caninum by ELISA, aborted. The relative risk for abortion among ELISA-positive heifers was 23.6. Abortion occurred predominantly between Days 120 and 152 gestation among the ELISA-positive heifers and throughout gestation among the ELISA-negative heifers. IFAT titres rose around the time of abortion in most of the heifers that were previously seropositive by ELISA, but dropped rapidly again in post-abortion samples. IFAT titres among 4/6 ELISA-positive heifers that did not abort increased, but later in gestation than the time other heifers aborted. IFAT titres remained negative in heifers that aborted that were ELISA negative. CONCLUSIONS: Heifers that were seropositive to N. caninum by ELISA had a much greater risk of abortion than seronegative heifers. Most seropositive heifers showed evidence of a reactivation of infection during pregnancy. High (> or =1:2,000) N. caninum IFAT titres also occurred in non-aborting heifers. CLINICAL RELEVANCE: Culling of replacement heifers seropositive to N. caninum may be a cost-effective strategy for minimising risk of abortion. Pregnancy testing heifers before 5 months gestation may overestimate the number that calve in N. caninum-infected herds, but would assist in documenting the occurrence of abortion. Reliance on a high (>1:2,000) IFAT titre to rule-in N. caninum as a cause of abortion is likely to produce false-positive results.     

Neospora caninum seropositivity and association with abortions in dairy cows in Mexico

The seroprevalence of Neospora caninum infection was estimated from a sample of 813 cattle from 20 dairy herds in five regions in Mexico. The true prevalence of infection was estimated to be 42% (95% CI: 39, 46). Seropositivity was associated with abortion (odds ratio (OR)=2.0) and was higher among cows raised on-farm (41%), than among replacement cattle purchased outside the farm (28%). The ORs relating abortion to seropositivity in individual herds ranged from 1.3 to 10. Overall, 26% of the abortions were attributed to N. caninum.     

Evaluation of the embryo transfer procedure proposed by the International Embryo Transfer Society as a method of controlling vertical transmission of Neospora caninum in cattle

OBJECTIVE: To evaluate efficacy of embryo transfer into seronegative recipients, using the procedure proposed by the International Embryo Transfer Society (IETS), for preventing vertical transmission of Neospora caninum in cattle. DESIGN: Prospective clinical trial. ANIMALS: 87 recipient cows and heifers and their embryo transfer calves from 22 donors originating from 9 dairy herds. PROCEDURE: Neospora caninum serologic status of donors and recipients was determined before collection and transfer of embryos. Viable embryos were washed and treated with trypsin. Recipients in experimental groups A (n = 50) and B (29) were seronegative and received embryos from seropositive and seronegative donors, respectively. Recipients in group C (n = 8) were seropositive and received embryos from seronegative or seropositive donors. Antibody titers against N caninum were determined monthly during pregnancy in recipients and in calf blood samples collected at birth. Tissues collected from stillborn calves and aborted fetuses were analyzed histologically and by immunohistochemical (IHC) methods. RESULTS: 76 calves and 11 fetuses and stillborn calves were examined. All calves from groups A and B were seronegative (n = 70) or lacked evidence of infection by use of tissue analysis (9). In group C, 5 of 6 calves were seropositive at birth, and IHC results were positive for 1 of 2 calves. Vertical transmission rate was significantly lower in groups A and B (0%) than in group C (75%). CONCLUSION AND CLINICAL RELEVANCE: Embryo transfer into seronegative recipients, using the procedure proposed by IETS, is an effective way to prevent vertical transmission of N caninum. Results provide support for pretransfer testing of all embryo transfer recipients.     

Chronic Neospora caninum infection and repeat abortion in dairy cows: a 3-year study

The serological status of Neospora was monitored in animals older than 6 months in a dairy herd with a 3-year history of prevalent N. caninum and N. caninum-associated abortions. The numbers of animals in the herd tested each year of the study period were 259, 222 and 231, respectively. A separate analysis was performed on the 122 animals persisting in the herd for the 3 years. The overall seroprevalence of N. caninum in the herd decreased from 31.7% in the first year to 24.8% in the second year and to 19.9% in the third year of the study, while the overall abortion rate decreased from 20.6% in the first year to 5.5% in the second year, and 9.9% in the third. These decreases occurred in response to control measures adopted from the second year onwards, such as culling Neospora-seropositive aborted animals and inseminating Neospora-seropositive dams with beef bull semen. Of the total number of abortions recorded in seropositive animals, 51% were repeat abortions that occurred in 36.8% of the animals with a previous history of abortion. The initial seroprevalence of Neospora in the 122 animals followed for the 3 years was 18%, increasing to 21.3% in the second and third years. Seroconversion only occurred in four animals during the second and third years of the study and abortion occurred only in seropositive individuals. Of the total number of abortions recorded in the 122 animals, 61.5% were repeat abortions that occurred in 26.7% of the animals with a previous history of abortion. These results indicate that Neospora seropositivity can be very stable through time and N. caninum infected cows can show a high rate of repeat abortions. The present data reinforce the idea that annual serological screening for Neospora can be an effective and rapid method of detecting N. caninum infection, such that control measures can be established at the farm level.